Screen printing is an old and established way of creating designs on various substrates, such as paper, metal, wood, glass, etc. Screen printing is essentially a method of printing where a stencil is formed by a screen, the screen is used to ink a substrate, and the substrate is then allowed to dry or cure as the case may be.
Early versions of screen printing used silk stretched over a wooden frame to form the screen. A design was created by painting the screen with a greasy medium. The pores of the silk were then closed using a suitable gum. The pores of the silk in the areas covered by the greasy medium were not closed because the greasy medium rejected the gum. Thereafter, the greasy medium was washed away with a solvent, such as turpentine, if paint was used as the greasy medium, resulting in the corresponding areas becoming pervious to ink. The screen was then placed on the surface of the substrate to be decorated and ink was applied through the screen to the surface using a rubber squeegee. The ink soaked through the pervious areas of the silk and was imprinted on the substrate.
More recent versions of screen printing use fine mesh screen materials rather than silk. The chosen screen material is coated with a photographic emulsion. The photographic emulsion is exposed to a suitable source of light, with the image to be reproduced being located between the light and the emulsion. The light causes the emulsion to harden except in areas where the image is located. Thereafter, the screen is washed to remove the emulsion from the areas where it has not been hardened by the light, i.e., the image areas. The screen is then ready to be used as a stencil to print a design on a substrate.
In modern time, screen printing has been widely used to create a variety of single and multi-colored designs on a variety of items, particularly clothing, such as T-shirts and sweatshirts. A known all-in-one screen printing machine is described in U.S. Pat. No. 5,622,108 and is available for such purposes. The '108 machine includes a cabinet mounted atop a stand. The upper portion of the cabinet and one side of the cabinet are open. An ultraviolet (UV) light source is positioned on the bottom of the cabinet and is positioned to shine UV light upward. The UV light source is suitable for exposing a photographic emulsion to create an image-bearing print screen. The print screen is held in a U-shaped frame. The U-shaped frame is supported in the cabinet by a shelf that extend inwardly from the three side walls of the cabinet. The U-shaped frame is rotatably coupled to the cabinet via a downward extending leg that engages a hole located in one corner of the cabinet shelf.
The '108 machine also includes a screw adjustment assembly and a fixed bevel block that work together to register the print screen into an optimal position. To cure the applied ink, the '108 machine provides a heating element in a shallow box-like housing. The housing is rotatably connected at one corner to an upper corner of the cabinet. The heating element is positioned in the housing so that heat is directed downward from the underside of the housing. To use the '108 machine, a print screen is formed using the UV light source. A substrate is place on a horizontal platen located within the cabinet near the cabinet upper opening. The print screen is placed directly over the substrate and ink is applied across the screen. The print screen is removed and the heating element housing is laterally rotated above the cabinet upper opening where heat is directed down onto the substrate. After the ink is cured, the heating element is laterally rotated away from the upper opening of the cabinet.
Although the '108 machine is a very useful all-in-one screen printing machine, a continued need exists for improving the system of registration. The present invention is directed to fulfilling this and other needs as described below.